1. Field of the Invention
The present invention relates to an electroluminescent (hereinafter referred to EL) display device in which images are displayed in a matrix fashion.
2. Description of Related Art
Conventionally, in an EL display device for displaying images in a matrix fashion, a data electrode array and a scanning electrode array are orthogonally arranged with each other to form a matrix on a glass substrate, sandwiching insulating layers and a luminescent layer between both arrays. Images are displayed with picture elements formed at each intersection of the data and scanning electrodes. Because the data electrode array and the scanning electrode array are arranged orthogonally with each other on a rectangular substrate, terminals for both electrode arrays are formed on two sides of the square substrate, respectively. These terminals for electrically connecting the electrodes to driver circuits are usually made of a metallic material. Therefore, regions on which the terminals are formed cannot be used for displaying images, and interfere with a viewer's sight if the terminals are formed on two sides of the substrate because the terminals have to be connected to the driver circuits. This is an obstacle in designing a display device.
With a purpose of solving the problem mentioned above, JP-A-7-263140 discloses an EL display device in which terminals for both data and scanning electrodes are formed on one side of a substrate by leading the scanning electrodes through a wiring lead portion to the side where the terminals are formed. However, there is another problem that a wiring resistance for each scanning electrode, when the electrode is made of a transparent conductive film such as ITO, cannot be made uniform because a lead wire length for each electrode is different from one another. The transparent ITO film which is readily available as a standard has a thickness of 0.2 .mu.m and a sheet resistance of 10 .OMEGA. per square. Also, there is a thickness limit at this moment and it cannot be made thicker than 1 .mu.m. In case this kind of ITO is used as transparent electrodes, its resistance will be more than 100 times higher than that of a metal such as aluminum. Accordingly, luminance uniformity of the display is adversely affected by the uneven wiring resistances of the scanning electrodes.